Resilient helix mount for traveling wave tube



June 7, 1966 A LONG ET AL 3,254,884

RESILIENT HELIX MOUNT FOR TRAVELING WAVE TUBE Original Filed June 28,1961 WEI E INVENTORS JAMES A. LONG MARSHALL B. Mc DONALD ATTORNEY UnitedStates Patent Office 3,254,884 Patented June 7, 1966 3,254,884 RESILIENTHELIX MOUNT FOR TRAVELING WAVE TUBE James A. Long, Los Altos, andMarshall B. McDonald, Palo Alto, Calif., assignors to Sylvania ElectricProducts Inc., a corporation of Delaware Original application June 28,1961, Ser. No. 120,228, now Patent No. 3,209,198, dated Sept. 28, 1965.Divided and this application June 30, 1965, Ser. No. 478,509.

1 Claim. (Cl. 267-1) This is a division of application Serial Number120,228, filed June 28, 1961, now Patent No. 3,209,198, grantedSeptember 28, 1965.

This invention relates to traveling wave tubes and in particular to animproved mounting structure for a rod mounted helix in a traveling wavetube.

The difficulty with mounting a helix and rod assembly within theenvelope of a traveling wave tube is providing uniform support for thehelix over its entire length. Unevenness in the tube wall and .in therods, even though within standard manufacturing tolerances, has anadverse effect on tube performance due to nonconcentricity of and unevenrod loading of the helix. Use of rods and tubular members havingextremely precise diameters tends to solve this problem but only atconsiderable increase in cost.

In accordance with this invention, rods and tubes having commercialtolerances can be used in traveling wave tube construction by providingan elongated undulating springlike element between any one or all of therods and the tube envelope. The spring element is formed to partiallyfit the contour of the rod so as to seat on the rod and has alongitudinal sinusoidal-like shape so that the element makes springlikecontact alternately with the envelope and rod at longitudinally spacedpoints along the tube. The spring element is fed into the envelope withthe helix and rod structure during assembly of the tube. and permitsremoval of the helix .and rod structure if disassembly is required. Asubstantially uniform pressure is exerted by the spring through the rodson the helix. Any unevenness in the diameters of the envelope wall andthe dielectric rods is averaged out by the springs so that the helix issupported substantiallyconcentrically on the axis of the tubenotwithstanding these irregularities. The spring strips may readily beformed by production techniques from standard strip stock and aretherefore very inexpensive to make and handle.

A general object'of this invention is the provision of a traveling wavetube with means for supporting the helix about the axis of the tubeutilizing commercially available tube envelopes and helix mount rods.

Another object is the provision of a rod mounted helix that is supportedthroughout its length with substantially constant radial force.

A further object is the provision of an extremely rugged helix-rodmounting structure by which movement of the helix is prevented by apositive longitudinally distributed force applied to the rods againstthe helix.

Still another object is the provision of resilient means forfacilitating insertion and removal of a helix-rod bundle into and from acommercial envelope and for preventing circumferential displacement ofthe bundle in the tube.

' These and other objects of our invention will becorr e apparent fromthe following description of a preferred embodiment thereof, referencebeing had to the accompanying drawings in which:

FIGURE 1 is a longitudinal section (partially schematic) of a travelingwave tube embodying our invention;

FIGURE 2 is an enlarged section taken on line 22 of FIGURE 1;

FIGURE 3 is a greatly enlarged portion of FIGURE 1 showing details ofthe spring construction;

FIGURE 4 is a section taken on line 4-4 of FIG- URE 3;

FIGURE 5 is a section similar to FIGURE 4 showing a modified form ofspring construction; and

FIGURE 6 is a line diagram illustrating the chord-like engagement of thespring with the interior of the envelope.

The traveling wave tube shown in FIGURE 1 comprises a tubular envelope10 which houses a gun structure 11 a at one end and a helix 12 Withinthe main body portion of reduced diameter. The helix 12 is supportedconcentrically of the axis A of the tube by three ceramic rods 13, 14and 15, see FIGURE 2, circumferentially spaced 12.0 degrees apart, andwhich make tangential engagement W1th successive turns of the helixthroughout the length of the helix. The gun'portion 11 of the tubeproduces an electron beam which passes axially down the tube and iscollected by the collector 17 at the opposite end. This beam interactswith radio frequency waves on the helix to transfer energy to the wavesin the well-known manner of a traveling wave tube.

The means for coupling the radio frequency waves to and from the helixhave been omitted for sake of clarity of the drawings.

The rods 13, 14 and 15, which may or may not be identical, extend fromrod mounts 18 and 19 near opposite ends of the tube and furnish theradial and longitudinal support for the entire helix. In accordance withthis invention, one or more of these rods is spaced from and supportedon the inner surface 10a of tube 10 by an elongated longitudinallyextending spring element 20 glitch extends a substantial portion of thelength of the e or.

Each spring element 20 comprises a single strip of spring metal and 'hasa longitudinally undulating configuration defining a series of roundedprojections 21 spaced apart by depressions 22. Each depression is formedwith a transverse concavely shaped seat 23 which engages a limitedportion of the periphery of the adjacent rod 13.. The projections 21bear against the inner surface of envelope 10 as shown more clearly inFIGURE 6, and exert a radially inward force against rod 13 which in turntransmits this force to the helix 12. This action of spring 20 iseffective throughout substantially the major portion of the length ofthe helix.

Since the length of each spring element 20 corresponds generally to thelength of the helix being supported, variations in dimensions andstraightness of the envelope 10 and of the helix support rod areaveraged out over the length of the spring element. The engagement ofthe spring element with envelope 10 and with the rod, while snug,permits sliding movement of the spring relative to the envelope and rodso that the axial length of the spring can vary slightly with changes inradial pressure along the spring and there is a substantially uniformlongiudinal distribution of radial forces exerted by the spring againsteach of the rods.

The semi-cylindrical concave seat 23 formed in each depression 22 of thespring elfectively locks the spring to the rod and insures its propercircumferential position with respect to the rod at all times. The widthof seat 23 may be less than the width of the spring "as shown in FIGURE4 or may be equal to the spring width as shown in FIGURE 5. 7

Spring elements 20 are inserted into the envelope simultaneously withinsertion of the rod and helix "structure into the tube. Each springelement is fed onto a rod as the latter is moved into the tube. Toprevent binding and to facilitate sliding action of the assembly duringthis operation, any lubricant suitable for use on vacuum elements,

such as alcohol, may be added. The uniform pressure of the springelement over its entire length against each rod serves to resist angulardisplacement of the rod within the tube. The uniform distribution ofradial force exerted by the springs against the rods centers the helixso that its is essentially concentric with the axis of the tube over thelength of the helix.

If disasseinbly of the tube is required, removal of the rod and helixstructure from one end of the tube is facilitated by the presence of thespring elements 20.

The projections 21 of the spring preferably are transversely straight sothat the outer spring surface 20a has a chord-like engagement with theenvelope inner surface 10a as shown in FIGURE 6. Thus the spring engagesthe envelope along the limited area at the spring edges 20c and 20d andtends to bite into the tube so as to resist circumferential displacementof the rod and helix. However, the limited engagernent area facilitateslongitudinal sliding relative to the envelope and greatly simplifiesassembly operations. When the tube is baked out during final stages ofassembly, spring edges 20c and 20d become embedded in the heat-softenedenvelope and are thus locked in position both longitudinally andcircumferentially. The entire helix-rod bundle is prevented fromshifting and a ruggedized construction is obtained.

Changes, modifications and improvements to the above described preferredembodiment of our invention may be made by those skilled in the artwithout departing from the spirit and precept of the invention. Thescope of the invention is defined in the appended claim.

We claim:

An elongated spring element having a sinusoidal-like shape withalternate outwardly extending longitudinally rounded projections andinwardly extending depressed portions, said projections beingtransversely fiat, each of said depressed portions having a longitudinalrecess.

References Cited by the Examiner UNITED STATES PATENTS 1,512,362 10/1924Phelps 2671,.5 1,811,012 6/1931 Hodge 267-1.5

ARTHUR L. LA POINT, Primary Eramz'ner.

W. B. WILBUR, Assistant Examiner.

